皆伐前后油松人工林下植物多样性变化及与土壤水分的关系

【目的】探讨油松人工林皆伐前后林下植物多样性的变化及与土壤水分的关系,为在油松林皆伐后植被恢复和发育阶段维持生物多样性、保持林分结构稳定、发挥更高生态效益等方面提供科学依据和经营措施建议。【方法】采用时序研究法,在河北平泉地区选择立地一致的不同林龄油松人工林(32年中龄林、40年近熟林、53年成熟林)和皆伐后不同时间(5、10、24 a)的天然更新林作为研究对象,分析不同生长发育阶段油松人工林下植物物种组成与多样性的变化规律及与土壤水分间的相关性。【结果】1)皆伐前后6种林分样地共出现灌木植物21种,草本植物65种,不同样地林下植物组成存在差异。胡枝子在各林分样地均有出现,且重要值均> 20%,在灌木层优势地位明显;草本层中菊科植物种类最多,有18种,其次是蔷薇科和禾本科,分别为6种和4种。2)不同林分样地林下植物多样性指数均表现为草本层>灌木层,皆伐前随着林龄增加林下植物多样性逐渐增加;皆伐后灌木层植物多样性表现为先下降后增加再下降,且变化幅度明显,伐后10 a灌木层Margalef丰富度指数、Simpson多样性指数、Shannon-Wiener多样性指数和Pielou均匀度指数最大,分别为1.40、0.61、1.24和0.74,与53年样地差异不显著。皆伐后不同时间的天然更新林草本层植物多样性均与伐前53年样地的差异不显著,皆伐对灌木层植物的影响较大。3)不同林地土壤水分变化规律较一致,表现为伐前随林龄增加而逐渐增加,伐后5~10 a仍保持较高水平,伐后24 a出现下降,经相关分析植物多样性指数与土壤水分之间有显著的正相关关系,与草本层的相关性达极显著水平。【结论】伐前林下植物多样性变化主要与林分密度降低、光照条件改善有关,伐后主要与油松天然更新及种间竞争有关。依靠油松天然更新恢复的林地保持了较高的生物多样性,但在皆伐10 a后出现下降的趋势,建议在此时对油松更新苗进行人工抚育、降低密度以维持植物多样性。土壤水分是影响植物多样性的关键生态因子,良好的土壤水分条件和林下植被的恢复和发展可以相互促进。

Variation of understory plant diversity and its relationship with soil moisture in Pinus tabulaeformis plantation before and after clearcutting

【Objective】The study aims to explore the variation of understory plant diversity and its relationship with soil moisture in Pinus tabulaeformis plantation before and after clearcutting,which has great significance for maintaining the biodiversity,maintaining the stability of the stand structure and exerting higher ecological benefits in vegetation restoration and development stages of the Pinus tabulaeformis forest after clearcutting.【Method】Pinus tabulaeformis plantation at different developmental stages(middle age forest of 32 years,near-mature forest of 40 years and mature forest of 53 years)and natural regeneration forest at different times after clearcutting(5 years,10 years and 24 years after clearcutting)in Pingquan area of Hebei Province were selected as research objects,the conditions of understory plants were investigated to analysis the variation of species composition and diversity of undergrowth plants in Pinus tabulaeformis plantations before and after clearcutting through chronosequence approach.【Result】1)There were 21 shrubs and 65 herbs in the six stand samples before and after clearcutting,and the plant composition varied in different plots before and after clearcutting.Lespedeza bicolor appeared in all stand samples,and the important values in each plot were>20%,which dominant position in the shrub layer was significant.There were 18 species of Compositae in herb layer,followed by Rosaceae and Gramineae,which were 6 and 4 species respectively.2)The diversity index of understory plants in different stand sample plots showed that herb layer>shrub layer.With the increase of forest age before clearcutting,the plant diversity increased gradually.After clearcutting,the plant diversity index showed a decrease firstly,then increased and decreased,and the change range was obvious.Margalef index,Simpson index,Shannon-Wiener index and Pielou index of shrub layer in 10 years after cutting were the highest,1.40,0.61,1.24 and 0.74,respectively,which was not significantly different from plot of 53 years.However,the plant diversity of herb layer of natural regeneration forests at different time after clear cutting was not significantly different from the pre-cutting forest land(53 years).This indicated that clearcutting has a greater impact on shrub plants.3)The variation of soil moisture in different forests was consistent,which showed that it increased gradually with the increase of forest age before cutting,and remained high in 5-10 years after cutting,and decreased after 24 years.There was a remarkable positive correlation between soil moisture factors and plant diversity index,especially with herb layer.【Conclusion】The variation of understory plant diversity pre-cutting was mainly related to the decrease of forest density and the improvement of illumination conditions,while the variation of understory plant diversity post-cutting was mainly related to natural regeneration and interspecific competition of Pinus tabulaeformis.The forest land which relied on the natural regeneration of Pinus tabulaeformis has maintained high biodiversity.It was suggested that the regeneration seedlings of Pinus tabulaeformis should be thinned artificially and the density should be reduced in time to maintain plant diversity in about 10 years after cutting.Soil moisture is a key ecological factor affecting plant diversity.Good soil moisture conditions and development of understory vegetation can promote each other.